Deborah H. Olster

Evolution of Bower Complexity and Cerebellum Size in Bowerbirds

To entice females to mate, male bowerbirds build elaborate displays (bowers). Among species, bowers range in complexity from simple arenas decorated with leaves to complex twig or grass structures decorated with myriad colored objects. To investigate the neural underpinnings of bower building, we examined the contribution of variation in volume estimates of whole brain (WB), telencephalon minus hippocampus (TH), hippocampus (Hp) and cerebellum (Cb) to explain differences in complexity of bowers among 5 species. Using independent contrasts, we found a significant relationship between bower complexity and Cb size. We did not find support for correlated evolution between bower complexity and WB, TH, or Hp volume. These results suggest that skills supported by the cerebellum (e.g., procedural learning, motor planning) contribute to explaining the variation in bower complexity across species. Given that male mating success is in part determined by female choice for bower design, our data are consistent with the hypothesis that sexual selection has driven enlargement of the cerebellum in bowerbirds.

Progesterone facilitation of lordosis in male and female Sprague-Dawley rats following priming with estradiol pulses

Adult male Sprague-Dawley rats rarely exhibit progesterone-facilitated lordosis following steroid treatments which are effective in females. In contrast, progesterone-facilitated lordosis has been observed following priming with estradiol pulses in another strain. The aim of this study was to compare progesterone-facilitated feminine sexual behavior in adult male and female Sprague-Dawley rats following priming with estradiol benzoate (EB) or estradiol pulses. Female sexual behavior was measured in adult, gonadectomized males and females treated as follows: Two pulses of estradiol followed by progesterone or oil the next day; EB (two doses) for 3 days, and progesterone or oil the next day. These protocols were repeated at 4- or 6-day intervals, respectively. Progesterone-facilitated lordosis was observed consistently in both sexes treated with estradiol pulses. By the fifth test, lordosis quotients did not differ between the sexes, but the lordosis ratings in progesterone-treated males remained lower than those observed in females. Proceptivity (hop-darting) was facilitated by progesterone in females, but was never observed in males. Lordosis was induced in both sexes by 15 micrograms EB, but was not reliably facilitated by progesterone. Treatment with the lower dose of EB (1.5 micrograms) induced high levels of receptivity in females (occasionally facilitated by progesterone), but not in males regardless of subsequent treatment (i.e, progesterone or oil). These data suggest that progesterone-facilitated lordosis can be induced in male Sprague-Dawley rats, if a regimen of estradiol pulses is used. Thus, the brain of the adult male is not inflexibly differentiated with regard to progesterone facilitation of feminine receptive behavior.

Intraventricular injection of neuropeptide Y antisera curbs weight gain and feeding, and increases the display of sexual behaviors in obese Zucker female rats

Obese Zucker rats are hyperphagic, overweight, and infertile. It has been postulated that neuropeptide Y (NPY) overproduction may contribute to obesity and infertility in these animals. To test this hypothesis, ovariectomized, adult obese Zucker rats were implanted with cannulae in the third ventricle and subsequently injected with NPY antisera or normal rabbit sera (NRS) 6, 4 and 2 h before experimental observation. Steroid-treated females injected with NPY antisera were significantly more receptive and were more likely to show proceptive behaviors than after treatment with NRS (e.g., lordosis quotient: NPY antisera, 65.5+/-6.9%; NRS, 30.9+/-11.6%, P < 0.02; 91% displaying proceptivity after NPY antisera injection vs. 36% after NRS, P < 0.03). Injection of NPY antisera also curbed food intake and weight gain (24 h food intake: NPY antisera, 10.5+/-2.1 g; NRS, 20.5+/-1.7 g, P < 0.01; 24 h weight gain: NPY antisera, -5.4+/-2.2 g; NRS, 5.8+/-0.7 g, P < 0.01). Locomotor activity was similar after NRS and NPY antisera treatment (P > 0.5) suggesting that general malaise was not responsible for the effects of NPY antisera on food intake or body weight. These data suggest that endogenous neuropeptide Y contributes to excessive feeding and weight gain, and suppressed reproductive behaviors in obese Zucker female rats.

Abnormal Estrous Cyclicity and Behavioral Hyporesponsiveness to Ovarian Hormones in Genetically Obese Zucker Female Rats1

Obese Zucker female rats are infertile. The present study was designed to assess estrous cyclicity in adult, ovary-intact, lean and obese Zucker rats and to compare reproductive behaviors induced by exogenous steroid hormones in ovariectomized (ovx) lean and obese Zucker rats. The majority (90%) of obese rats had incomplete cycles in comparison with the normal, 4-day cycles displayed by lean Zucker rats. After ovariectomy, all rats were treated with estradiol benzoate (EB, 15–100μ g/kg) or EB plus progesterone (P, 2–20 mg/kg), and tested for sexual receptivity and proceptivity (PRO). At the highest EB dose, obese Zucker females displayed lordosis less frequently than lean rats (lordosis quotient, LQ, 8 ± 6% vs. 32 ± 13%, respectively). At the lowest doses of EB plus P, lean females were extremely receptive and proceptive (LQ = 93 ± 4%, PRO = 6.2 ± 2 bouts/min). Zucker obese females, in contrast, were only slightly receptive (LQ = 26 ± 11%) and showed less PRO than lean rats (PRO = 2.4 ± 0.6 bouts/min). In...

Biochemical and Immunocytochemical Assessment of Neural Progestin Receptors Following Estradiol Treatments that Eliminate the Sex Difference in Progesterone-Facilitated Lordosis in Guinea-pigs

A single injection of estradiol benzoate (10 μg), while highly effective in ovariectomized female guinea‐pigs, does not prime castrated males to display progesterone‐facilitated lordosis. In contrast, adult males and females exhibit the same, high degree of progesterone‐facilitated lordosis when primed with two, 2.0 μg injections of free estradiol‐17ß (pulse regimen). We compared neural progestin receptor induction after these different estradiol treatments by in vitro radioligand binding assays and immunocyto‐chemistry. Binding assays confirmed previous observations of lower concentrations of cytosol progestin receptors in the mediobasal hypothalamus‐preoptic area in estradiol benzoate‐treated males than in females. No such sex difference was observed in animals that had been exposed to the behaviorally effective estradiol pulse regimen; rather, hypothalamic‐preoptic area progestin receptor concentrations in these animals did not differ from the low levels observed in males treated with the behaviorally ineffective estradiol benzoate regimen. Immunocytochemical analysis revealed progestin receptor‐immunoreactivity in fewer cells in the medial preoptic nucleus‐anterior hypothalamic nucleus, periventricular preoptic area and arcuate nucleus of estradiol pulse‐ as compared to estradiol benzoate‐treated males and females. Estradiol benzoate treatment induced progestin receptor‐immunoreactivity in more cells in the medial preoptic area and ventrolateral hypothalamus than estradiol pulses in males, but not in females. Surprisingly, in these regions estradiol benzoate‐treated males had significantly more progestin receptor‐immunoreactive cells than females.

Development of progesterone-facilitated lordosis in female guinea pigs: relationship to neural estrogen and progestin receptors

Ovariectomized (OVX), 20-day-old female guinea pigs did not exhibit lordosis following treatment with estradiol benzoate (EB) and progesterone. Behavioral responsiveness to EB and progesterone developed abruptly; by 30 days of age, responses typical of adult females (greater than 9 weeks of age) were observed. In vitro assays of neural steroid receptors were performed to test the hypothesis that a deficiency in the concentration of hypothalamic and/or preoptic area estrogen and/or progestin receptors contributes to the lack of progesterone-facilitated lordosis in juvenile (20-day-old) females. Assay of cytosol progestin receptors in the mediobasal hypothalamus (MBH) and preoptic area (POA) of immature and adult females 40 h after injection of EB confirmed a previous report that the concentration of estradiol-induced cytosol progestin receptors in the MBH of juvenile females was slightly lower than that observed in adults. Furthermore, MBH cell nuclear accumulation of progestin receptors after progesterone injection was markedly lower (i.e. 42%) in immature, as compared to adult females. The concentrations of cytosol estrogen receptors in the MBH and POA did not differ between immature and adult OVX guinea pigs. Also, cell nuclear estrogen receptor accumulation in the MBH after estradiol injection was comparable in immature and adult females. These data suggest that a deficiency in cell nuclear progestin receptor accumulation in the MBH may contribute to the absence of progesterone-facilitated lordosis in estradiol-primed, immature female guinea pigs. This age-related difference in cell nuclear progestin receptor accumulation may be due, in part, to reduced concentrations of estradiol-induced cytosol progestin receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of alcohol on the sexual motivation of the male rat

Previous research measuring the effects of alcohol on sexual behavior has primarily focused on its effects on copulation. The present experiment was designed to investigate the effects of alcohol on the sexual motivation of the male rat by requiring operant responding to gain access to a sexually receptive female. A novel apparatus was used that allowed both visual and olfactory cues from an estrous female to reach the male. Lever presses resulted in the opening of a door that permitted the male rat to enter an adjacent chamber where a receptive female was located. Treatment with low to moderate doses of alcohol (0.5 g/kg and 1.0 g/kg) resulted in increased latencies to emit the first response of the males working for access to females, but did not affect response rate or subsequent mount or ejaculation latencies, when these males were allowed access to the receptive female. Furthermore, alcohol failed to show any response-reinstating or disinhibitory effects when tested following a period of nonreinforced extinction trials. An additional experiment, in which rats received equivalent doses of alcohol, revealed no decrease in spontaneous locomotion. Taken together, these data suggest that the response-reducing effects of alcohol are probably not a result of general drug-induced reductions in activity, but rather an attenuating action of the drug on sexual motivation.

Colchicine-lnduced Accumulation of Estrogen Receptor and Progestin Receptor Immunoreactivity in Atypical Areas in Guinea-Pig Brain

Using immunocytochemical techniques, cells containing estrogen and progestin receptors have been observed in many discrete regions of the guinea‐pig forebrain, including the mediobasal hypothalamus and preoptic area. While most reaction product is located within cell nuclei, we have reported abundant reaction product in perikaryal cytoplasm and neuronal processes as well. Ultrastructural analysis has revealed the presence of estrogen and progestin receptors in atypical subcellular sites within the hypothalamus, including dendrites and axon terminals. In order to determine if microtubule‐dependent intracellular transport is involved in intraneuronal transport of steroid hormone receptors, ovariectomized guinea‐pigs were injected intracerebroventricularly with the microtubule inhibitor, colchicine, and brain sections at the level of the hypothalamus were immunostained for estrogen receptors. This treatment resulted in the appearance of estrogen receptor immunoreactivity in the paraventricular and mediodorsal thalamic region, areas typically devoid of estrogen receptor‐immunoreactive cells in guinea‐pigs. In a second study on progestin receptors, we observed the colchicine‐induced accumulation of progestin receptor immunoreactivity in the paraventricular thalamic, mediodorsal thalamic and lateral dorsal thalamic areas as well as in the medial amygdala, all areas typically devoid of progestin receptor immunoreactivity. While estradiol injection induced progestin receptor immunoreactivity in the hypothalamus and preoptic area as described previously, it had no effect on the colchicine‐induced accumulation in the thalamus and amygdala. These results provide evidence that in some neurons, progestin receptors and estrogen receptors are transported intracellularly, apparently at a rapid enough rate that they do not ordinarily accumulate within the perikaryon.

Opioid Receptor Blockade Promotes Weight Loss and Improves the Display of Sexual Behaviors in Obese Zucker Female Rats

Obese Zucker female rats are hyperphagic, overweight, infertile, and hyporesponsive to the inductive effects of ovarian steroid hormones on sexual behaviors. It has been postulated that endogenous opioid activity may contribute to their obesity and reproductive dysfunction. To test this hypothesis, ovariectomized, adult obese Zucker rats were treated with the opioid receptor antagonist, naltrexone, or saline prior to measurement of steroid-induced sexual behaviors, food intake, and body weight. In estradiol benzoate (EB)-treated rats, naltrexone injection increased the display of sexual receptivity (lordosis quotient, LQ: saline, 11+/-10%; 5 mg/kg naltrexone, 54+/-15%, p < 0.05) and also elicited proceptivity (PRO), which was never observed after saline injection. In EB plus progesterone-treated animals, naltrexone administration enhanced both sexual receptivity and proceptivity (LQ: saline, 17+/-10%; 5 mg/kg naltrexone, 96+/-3%; p < 0.05; PRO: saline, 3.0+/-2.4 bouts/min; 5 mg/kg naltrexone, 45.3+/-12 bouts/min; p < 0.01). Naltrexone injection also decreased 24-h food intake (saline, 24.2+/-0.7 g; 5 mg/kg naltrexone, 17.6+/-1.2 g; p < 0.05) and weight change (saline, +7.3+/-0.8 g; 5 mg/kg naltrexone, -4.5+/-1.4 g, p < 0.01). Morphine treatment blocked these effects of naltrexone on sexual behaviors, food intake, and body weight. These data suggest that endogenous opioids contribute to hyperphagia, obesity, and behavioral hyporesponsiveness to ovarian steroid hormones in obese Zucker rats.

Children’s Vocal Properties as Mobilizers of Stress-Related Physiological Responses in Adults

We measured the ways that women with varying degrees of perceived power respond physiologically to children’s elevated vocal pitch (F 0 : fundamental frequency), a social dependence/immaturity cue. Listeners believed either that they would provide instructions or make judgments about the children they heard. As predicted, women with low perceived power in caregiving relationships (i.e., who attributed greater power to children than to self) were highly reactive to children’s pitch properties—in particular, when they anticipated providing instructions. When expecting to provide instructions to children with higher F 0 voices, women with low perceived power showed elevations in cortisol levels and heart rate (consistent with defensive mobilization for threat). In all other pairings of women and children, cortisol and heart rate levels held relatively constant or declined. In addition, women with low perceived power showed better recall of messages from children with higher F 0 voices than lower F 0 voices. Implications are drawn for interaction patterns that foster caregiving stress and conflict.